Clinching punch and apparatus

ABSTRACT

A clinching apparatus includes a clinching punch having a specifically dimensioned tapered surface which improves the strength of a clinch joint created therewith. In another aspect, a tapered surface adjacent a distal end of a clinching punch has an angle of 20-35° relative to a distal end. A further aspect of a clinching apparatus provides a tapered surface adjacent a distal end which is configured in accordance with a specific formula.

BACKGROUND AND SUMMARY

The present invention relates generally to clinching apparatuses and more particularly to a clinching punch and joint formed therewith.

It is known to use a punch and die to create a clinch joint between workpiece sheets. Such a device is disclosed in U.S. Pat. No. 5,177,861 entitled “Apparatus for Joining Sheet Material” which issued to Sawdon on Jan. 12, 1993, and is commonly owned with the present application. This patent is incorporated by reference herein. This prior device was a significant step in the industry but there is still room for further improvements.

Another clinching construction is disclosed in U.S. Pat. No. 5,727,302 entitled “Die and Punch for Forming a Joint and Method of Making the Die” which issued to Sawdon on Mar. 17, 1998, and is commonly owned with the present application. This is also incorporated by reference herein. This prior punch includes a 5° frusto-conical taper which was intended to advantageously prevent high stress concentrations and to improve the tool life during high pressure tool flexure misalignments.

In accordance with the present invention, a clinching apparatus includes a clinching punch having a specifically dimensioned tapered surface which improves the strength of a clinch joint created therewith. In another aspect, a tapered surface adjacent a distal end of a clinching punch has an angle of 20-35 degrees relative to a distal end. A further aspect of a clinching apparatus provides a tapered surface adjacent a distal end which is configured in accordance with a specific formula. Additional advantages and features of the present clinching apparatus can be ascertained from the following description and appended claims taken in conjunction with the present drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view showing a clinching apparatus;

FIG. 2 is a cross-sectional view, taking along line 2-2 from FIG. 1, showing the clinching apparatus;

FIG. 3 is a perspective view showing a punch employed in the clinching apparatus;

FIG. 4 is a side elevational view showing the punch;

FIG. 5 is an enlarged side elevational view, taken within circle 5 from FIG. 4, showing the punch;

FIG. 6 is an end elevational view showing the punch; and

FIG. 7 is an enlarged diagrammatic view showing a clinch joint formed using the clinching apparatus.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a clinching apparatus 11 includes a punch assembly 13, a die assembly 15 and material workpiece sheets 17 and 19. Punch assembly 13 includes a punch holder 21, a hollow stripper retainer 23, a stripper 25, a helically coiled spring 27 and a punch 29. Retainer 23 is affixed to a periphery of holder 21, and stripper 25 is a hollow member, a section of which is linearly moveable through an aperture 31 of retainer 23. An axial length of stripper 25 is preferably greater than twice the diameter of an abutment flange 32 thereof. Spring 27 is located between flange 32 of stripper 25 and a facing surface of holder 21 so as to urge stripper 25 axially away from holder 21 but also allow stripper 25 to be compressed toward holder 21 during clinch joint forming when punch 29 is linearly advanced along its centerline and axial direction by a fluid powered actuator moving holder 21 and/or its attached frame. Exemplary actuators for moving either the punch or die are discussed in U.S. Pat. No. 6,115,898 entitled “Force Multiplying Apparatus for Clamping a Workpiece and Forming a Joint Therein” which issued to Sawdon on Sep. 12, 2000, and U.S. Pat. No. 8,650,730 entitled “Clinching Tool” which issued to Sawdon on Feb. 18, 2014, both of which are incorporated by reference herein.

Die 15 includes a body 41, and a fixed and stationary anvil 43 integrally upstanding from body 41. Furthermore, die 15 additionally includes a circular-cylindrical shield 45 attached to body 41 with a set of three movable die blades 47 located between a generally cylindrical side of anvil 43 and shield 45. A coiled spring 49, elastomeric O-ring or other biasing member is located between shield 45 and blades 47 so as to urge distal ends of the die blades toward the side of anvil 43. Punch holder 21 and die body 41 are fastened to a C-frame, fixture or other mechanism such that punch 29 and anvil 43 are always intended to be aligned with each other in all joint forming operating conditions in the preferred embodiment of the present punching apparatus.

Reference should now be made to FIGS. 2-6. Punch 29 includes a generally circular-cylindrical body 61 which is elongated in an axial direction defined by a centerline CL of the punch. A recess 63 has an axially elongated shape machined in a peripheral surface of body 61 with a partially spherical depression 65 located at a trailing end thereof. A threaded fastener 67 and surrounding partially spherical retention ball or collar 69 engage with recess 65 to secure punch 29 to holder 21 in a removable manner such that a proximal or trailing end 71 of punch 29 firmly abuts against holder 21.

Punch 29 further includes a clinch joint-forming tip 81 which ends in a distal or leading end 83. Tip 81 of punch 29 further includes a generally circular-cylindrical peripheral side surface 85 which is located between distal end 83 and an arcuately curved transition section 87. Distal end 83 and a section with surface 85 are the portions of punch 29 that enter into and create a recessed cup for the clinch joint in a punching and deforming action. It is noteworthy that surface 85 has a generally constant diameter B without any discontinuities or steps therein. Alternately, a very small draft angle can be provided on surface 85, but generally equal to 5° relative to the punch centerline. Moreover, arcuately curved section 87 may alternately have a frusto-conical shape thereto although various workpiece deformation or punch strength benefits may not be achieved.

A frusto-conical taper 101, annular in an end view, is located between distal end 83 and cylindrical side surface 85. Taper 101 preferably has an angle F of 20-35 degrees relative to end 83, more preferably 28-32 degrees, and most preferably 30 degrees for two workpieces 17 and 19 of differing thicknesses. Intersecting lines defined between sidewall surface 85, taper 101 and distal end 83 all have angular corners in one version, however, it is alternately envisioned that one or both of the intersecting corners can employ a radius no greater than 0.02 inch. Furthermore, N is a sidewall neck thickness NL or NR of punch-side workpiece 17, A is an axial length of body 61 of punch 29, E is a minor radius measured between centerline CL of punch 29 and an intersection between tapered surface 101 and distal end 83, t₁ is a minimum thickness of punch-side workpiece 17 at the bottom or button of the final clinch joint, and t₂ is a minimum thickness of die-side workpiece 19 at the bottom or button of the final clinch joint.

Additionally, angle F for taper 101 of punch 29 is preferably determined according to the following formula regarding the desired final clinch joint 111 as illustrated in FIG. 7:

$E = {\frac{B}{2} - {\frac{P_{thk}}{2}\left( \frac{1}{\tan \mspace{11mu} F} \right)}}$

where 2E is a minor diameter of side surface 85 where the tapered surface intersects distal end 83, B is a major diameter of side surface 85 where tapered surface 101 intersects side surface 85, P_(thk) is a nominal (unclinched) punch-side workpiece 17 material thickness, and F is the angle of tapered surface 101.

The angular dimensions for the present taper 101 have been found to be significantly superior in joint performance as compared to conventional punch tips which have no taper or a mere 5° transitional taper, especially for a workpiece arrangement where punch-side workpiece 17 is less than half the nominal thickness of die-side workpiece 19 as measured prior to joint formation. One such arrangement is where workpieces 17 and 19 are mating components or housings in a refrigerator appliance, or alternately an oven appliance, a dish washer appliance, a clothes washer appliance, a clothes dryer appliance or the like. The specific tip dimensional ranges disclosed herein have been found to better control the workpiece material flow throughout the duration of the material joining process, especially creating a more constant and thicker punch-side workpiece thickness NL and NR at the most inwardly constricted diameter 113 of die-side workpiece 19 where the workpieces interlock together after full clinch joint formation. The further interlocking deformation areas are at LL and LR. In contrast, a traditional punch with no taper at the end-to-sidewall transition is prone to causing undesired tearing or piercing of the punch-side workpiece adjacent constricted diameter 113.

By way of further comparison for one example of the present apparatus, workpieces 17 (HRB 55, textured pre-painted) and 19 (HRB 60) are both steel, where the punch-side workpiece has a nominal thickness of 0.19 inch and the die-side workpiece has a nominal thickness of 0.40 inch, clinched together by a punch with taper angle F of 30°. This construction was found to have a finished clinch joint peel strength of at least 25 pounds of force and with a shear strength of at least 75 pounds, while the conventional and untapered punch version had a peel strength of less than 15 pounds of force. In another example, 0.026 inch nominally thick stainless steel (HRB 71) was used for punch-side workpiece 17 with HRB 55 steel of 0.40 inch nominal thickness for die-side workpiece 19; this generated a peel strength of at least 60 pounds and a shear strength of at least 185 pounds for a 30° taper angle F on punch 29. In these examples, a diameter C_(B) of a clinch joint outer button circular periphery is 0.188 inch, a button cap height Z is 0.038 inch, and a total button bottom thickness X is 0.021 inch. Furthermore, the preceding examples employed punch 29 with dimensions of A=3.937 inch, B=0.120 inch, C_(p)=0.480, E=0.044, F=30° and G=0.015 inch. It should be appreciated that these dimensions are simply exemplary and the dimensions may vary (although the joint performance may also then vary).

While the preferred embodiment of the present clinching apparatus has been disclosed, it should be appreciated that other variations are possible. For example, while three movable die blades have been disclosed, it should be appreciated that two, four or other quantities of die blades surrounding or partially surrounding an anvil of the die assembly may be employed although certain advantages of the present die may not be realized. Furthermore, a punch of a polygonal body periphery can alternately be used although certain manufacturing and cost advantages may not be obtained. The shapes of the punch holder, stripper, spring and stripper retainer can be varied, however, various advantages may not be realized. A moving anvil, fixed die blades, and the absence of the disclosed shield may alternately be used, although such an arrangement would forego many advantageous features of the present device. Additionally, aluminum and other workpiece materials may be employed with the present clinching apparatus although the exact dimensions may need to be slightly varied to account for the material flow differences. It should be appreciated that other modifications and variations may be made to the preferred apparatus without departing from the spirit and scope of the present invention. 

The invention claimed is:
 1. A clinching apparatus comprising a clinching punch including a substantially cylindrical side surface and a substantially flat clinch joint-forming distal end, a frusto-conically tapered surface located between the side surface and the distal end, the tapered surface having an angle of 20-35 degrees relative to the distal end.
 2. The clinching apparatus of claim 1, wherein the punch further includes an elongated body having a substantially cylindrical section coaxially aligned with the side surface and a curved surface directly connecting the side surface to the body.
 3. The clinching apparatus of claim 1, wherein the entire portion of the side surface, which is adapted to form an inside cup of a clinch joint, has a substantially uniform diameter free of any step thereon.
 4. The clinching apparatus of claim 1, wherein the angle of the tapered surface is 28-32 degrees relative to the distal end.
 5. The clinching apparatus of claim 1, wherein intersecting lines, defined by the tapered surface and the adjacent side surface and the distal end, are corners free of radii.
 6. The clinching apparatus of claim 1, wherein the punch includes a fastener-engagable recess located in a side of a body, further comprising a punch holder to which the punch is removably fastened.
 7. The clinching apparatus of claim 1, further comprising: a holder secured to a proximal end of the punch; a stripper surrounding a portion of the punch and being moveably coupled to the holder; a spring biasing the stripper away from the holder; and a clinching die coaxially aligned with the punch and including a central anvil, movable die blades and a biasing member urging the die blades toward the anvil.
 8. The clinching apparatus of claim 1, wherein the side surface and tapered surface are dimensioned according to: $E = {\frac{B}{2} - {\frac{P_{thk}}{2}\left( \frac{1}{\tan \mspace{11mu} F} \right)}}$ where 2E is a minor diameter of the side surface where the tapered surface intersects the distal end, B is a major diameter of the side surface where the tapered surface intersects the side surface, P_(thk) is a nominal punch side-workpiece material thickness, and F is the angle of the tapered surface.
 9. The clinching apparatus of claim 1, further comprising sheet metal workpieces clinched together by the punch and the die, at least one of the workpieces being less than half of the thickness of another of the workpieces, and a clinch joint formed therebetween withstanding a peel force of at least twenty-five pounds.
 10. A clinching apparatus comprising a clinching punch including a substantially cylindrical side surface and a substantially flat clinch joint-forming distal end, a frusto-conically tapered surface located between the side surface and the distal end, the tapered surface has an angle F; wherein the side surface and tapered surface are dimensioned according to: $E = {\frac{B}{2} - {\frac{P_{thk}}{2}\left( \frac{1}{\tan \mspace{11mu} F} \right)}}$ where 2E is a minor diameter of the side surface where the tapered surface intersects the distal end, B is a major diameter of the side surface where the tapered surface intersects the side surface, P_(thk) is a nominal punch side-workpiece material thickness, and F is the angle of the tapered surface.
 11. The clinching apparatus of claim 10, further comprising: a holder secured to a proximal end of the punch; a stripper surrounding a portion of the punch and being movably connected to the holder; a spring biasing the stripper away from the holder; and a clinching die coaxially aligned with the punch and including a central anvil, movable die blades and a biasing member urging the die blades toward the anvil.
 12. The clinching apparatus of claim 11, further comprising a clinch joint in multiple sheet metal workpieces, created between the punch and the die, the workpieces being part of an appliance.
 13. The clinching apparatus of claim 10, wherein the entire portion of the side surface, which is adapted to form an inside cup of a clinch joint, has a substantially uniform diameter free of any step thereon.
 14. The clinching apparatus of claim 10, wherein the angle of the tapered surface is 28-32 degrees relative to the distal end.
 15. The clinching apparatus of claim 10, further comprising sheet metal workpieces clinched together by the punch and die, at least one of the workpieces being less than half of the thickness of another of the workpieces, and a clinch joint formed therebetween withstanding a peel force of at least twenty-five.
 16. A clinching apparatus comprising: a linearly movable clinching punch including a side and an end, a taper located between the side and the end, the taper having an angle of 20-35 degrees relative to the end and the taper including an annular end view shape; the side, which is adapted to form an inside cavity of a clinch joint, being free of any step thereon; a holder secured to a proximal end of the punch; a stripper located adjacent a portion of the punch; a resilient member biasing the stripper away from the holder; and a clinching die including a central anvil coaxially aligned with the punch, and upstanding die blades surrounding the anvil.
 17. The clinching apparatus of claim 16, wherein the side and taper are dimensioned according to: $E = {\frac{B}{2} - {\frac{P_{thk}}{2}\left( \frac{1}{\tan \mspace{11mu} F} \right)}}$ where 2E is a minor diameter of the side where the taper intersects the end, B is a major diameter of the side where the taper intersects the side, P_(thk) is a nominal punch side-workpiece material thickness, and F is the angle of the taper.
 18. The clinching apparatus of claim 16, further comprising a clinch joint in multiple appliance workpieces, created between the punch and the die.
 19. The clinching apparatus of claim 16, further comprising a clinch joint created in sheet steel workpieces between the punch and the anvil.
 20. The clinching apparatus of claim 16, further comprising a clinch joint created in sheet aluminum workpieces between the punch and the anvil.
 21. The clinching apparatus of claim 16, wherein the angle of the taper is 28-32 degrees relative to the end. 